There is an urgent need for the evaluation of innovative web-based data collection methods that are conven- ient for the general public and yield high-quality scientific information for population researchers. The vast ma- jority of all Americans between the ages of 15 and 49 now use the Internet, even across historically marginal- ized groups such as the poor. Scientific advance has been equally rapid in: 1. Web-based survey data collection tools, giving us tremendous knowledge of the strengths and weak- nesses of using the Internet for scientific data collections. 2. The survey methodology of maximizing response to data collection efforts under fixed constraints and understanding non-response bias across measures within the same survey, including the tools for con- ducting web-based data collection that minimizes non-response bias. These rapid advances in knowledge of how the Internet might be used to conduct large-scale, high-quality sci- entific data collections are especially important to demographers researching population health. The rising costs of data collections are threatening the future of national face-to-face surveys of the general population. This issue is of high significance to all NIH-supported research on the general population, but it is especial- ly high priority for reproductive health research on topics such as contraceptive use and non-use. NIH R01 budget caps have remained exactly the same for more than 25 years, in spite of both inflation and the rapidly rising costs of data collection. As a result, new primary data collections using face-to-face interviewing of na- tional samples are now a rare, large-scale team enterprise in the population sciences, and one that is almost impossible to support using the R01 mechanism. Even the few remaining national studies using face-to-face survey data collection are now threatened, because the continued increases in costs are likely to render them difficult to support within another decade. The development of an alternative, scientifically sound data collec- tion methodology that is both well-aligned with emerging web-based technologies and convenient for the gen- eral public is absolutely essential for the continuation of high-quality population research on evolving high- priority health and well-being issues in the U.S. population. We propose to develop an optimal web-based approach to conducting national survey data collection, and validate the approach against a current gold-standard national survey of reproductive health that relies on in- terviewer-administered data collection (the U.S. National Survey of Family Growth, or NSFG). This work will allow us to determine the ability of a national web-based survey that employs an address-based sample and both sequential mixed-mode and modular survey design techniques (i.e., completing a survey in several short- er sessions rather than a single longer session) to replicate the content in this survey as well as national face- to-face survey estimates across a range of reproductive health topics using a more cost-efficient design.